Micro positioning device

ABSTRACT

A device for providing micro positioning having an operating range in the submicron order in the X and Y directions, respectively. Positioning is achieved by depositing a pair of aluminum electrodes on a piezoelectric element bonded on a silicon wafer, vertically moving the piezoelectric element, arranging a plurality of micro actuators whose contact pin ends, formed on the aluminum electrodes, rotate on a surface as an array, and displacing in the horizontal direction a moving member arranged on the micro actuator array.

FIELD OF THE INVENTION

The present invention relates to a micro positioning device capable offinely positioning a member such as a roller in the X and Y directions.

BACKGROUND OF THE INVENTION

The attempt to compact existing mechanical systems has a rather longhistory. However, a technology has recently drawn attention to integratea mechanical system of a size that varies from several micrometers toseveral hundreds of micrometers. It comprises a plurality of componentssuch as sensors, actuators, and electronic circuits, and preferably usethe IC (Integrated Circuit) fabrication technique called MEMS (MicroElectro Mechanical Systems). Sensors in the field of MEMS are fastreaching the level of practical use, mainly as acceleration sensorsusing transducers, as described in the paper by H. Seidel, et al,"Capacitive Silicon Accelerometer with Highly Symmetrical Design",Transducers '89 Lecture No. B10.4, June 1989, and as pressure sensors,described in the paper by K. Ikeda, et al, "Silicon Pressure SensorIntegrates Resonant Strain Gauge On Diaphragm", Transducers '89 LectureNo. B4.3, June 1989. However, the study of micro actuators has justbegun. As an example of a micro actuator, an ultrasonic motor using apiezoelectric element is actively studied at present.

OBJECTS AND SUMMARY OF THE INVENTION

The positioning accuracy of detectors in an optical recording ormagnetic recording system may be in the future of the order ofsubmicrons. It requires that the positioning device used for the systemhave an operating range of several hundreds of micrometers in the X andY directions, respectively, that its size does not exceed severalmillimeters and, finally, that it get a quick response. Positioningmeeting the above requirement can be achieved with a conventional microultrasonic motor.

Accordingly, it is an object of the present invention to provide adevice capable of achieving fine positioning.

It is another object of the present invention to achieve micropositioning of the order of 100-μm in the X and Y directions.

It is a further object of the present invention to arrange, on the samesurface, micro actuators of the order of micrometers using semiconductorfabrication techniques and capable of surface-driving the group ofactuators with a driving source.

The micro positioning device of the present invention, as describedhereinafter comprises: a substrate, a plurality of micro actuatorsarranged on the substrate, and a moving member placed on the microactuators. Each micro actuator consists of a driving section forapplying a driving force to excite vertical motion on the substrate, anda mechanism for converting vertical motion into rotational motion,displaced in the horizontal direction. The structure of the microactuator which is the basic component of the present invention differsin terms of the type of driving force used, as will be shownhereinafter.

The foregoing and other objectives, features and advantages of thepresent invention will become clearer from the detailed descriptions ofthe preferred embodiments of the invention, as illustrated in theaccompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an embodiment of the micro actuator 60 structure accordingto the present invention;

FIG. 2 shows a second embodiment of the micro actuator structure inaccordance with the present invention;

FIG. 3 shows still another embodiment of the micro actuator structure ofthe present invention;

FIGS. 4a-4e show the fabrication process of the micro actuator in FIG.2;

FIGS. 5a-5d show the fabrication process of the micro actuator in FIG.3;

FIGS. 6a-6e and 7a-7d show the operating principle of the presentinvention; and

FIG. 8 shows a schematic structural diagram of the micro positioningdevice according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows the structure of a micro actuator using vibration force asits driving force. A piezoelectric element (PZT) 2 is bonded orlaminated to substrate 1, (e.g. a silicon wafer). Aluminum electrodes 3Aand 3B are deposited on the PZT 2, and a contact pin 4 is formed acrossthe aluminum electrodes. Although polyimide is used for contact pin 4 inthis particular embodiment, it may be possible to use resist whichallows the pin to have a large aspect ratio.

FIG. 2 shows the structure of a micro actuator 40 using Coulomb's forceas the driving force. Operation of the micro actuator using Coulomb'sforce will be further described hereinafter. FIGS. 4(a)-4(e) show thefabrication process steps for the driving section 45 of the microactuator 40. Note that the driving section 45 as shown upon completionin FIG. 4(e) excludes contact pin 4, as illustrated in FIG. 2.

A silicon nitride film is first deposited on a silicon wafer 1. As shownin FIG. 4(a), the silicon nitride film is etched to form a desiredpattern 5. Then, steam is applied to silicon wafer 1 to oxidize theetched section 8 to produce the structure shown in FIG. 4(b). Next,additional silicon nitride is deposited on the silicon wafer 1 to form afirst silicon nitride film 5', a polycrystal silicon film 6 is depositedon the first silicon nitride film 5', and a second silicon nitride film5" is deposited on the polycrystal silicon film 6. Following depositionof these layers 5', 6 and 5", the central portion 50 of the layers 5',6, 5" is etched to a predetermined size to form the structure of FIG.4(c). Next, the portion 8 is etched at the central section 50 so as toform an opening through the central section 50 to the portion 8, asshown in FIG. 4(d). Subsequently, the silicon wafer 1 is oxidized andoxide films 7 are formed, as shown in FIG. 4(e). The micro actuator 40with the structure shown in FIG. 2 is obtained by forming the contactpin 4 on the driving section 45 thus fabricated.

FIG. 3 shows the structure of a micro actuator 70 using fluid pressure(e.g., air pressure) as its driving force. In this case, the drivingsection 75 of the micro actuator 70, which excludes the contact pin 4illustrated in FIG. 3, is fabricated using the process steps shown inFIGS. 5(a)-5(d).

Silicon nitride films 11 are deposited on both sides of a first siliconwafer 1A. A desired pattern is then formed by lithographic techniquesand followed by selective etching. Similarly, a silicon nitride film 11is deposited on both sides of a second silicon wafer 1B and a desiredpattern is likewise formed by lithographic techniques. It is then etchedas shown in FIG. 5a in a manner similar to the process used for thefirst silicon wafer 1A. An anisotropic etching is then applied to thefirst silicon wafer 1A to form an air channel 9 (FIG. 5b). Likewise,anisotropic etching is also applied to the second silicon wafer 1B in amanner similar to the process used for the first silicon wafer 1A. Init, a wedge shaped pattern acting as a valve for fluid such as air isformed at the central portion of the second silicon wafer 1B (FIG. 5b).

Referring to FIG. 5c, the silicon nitride film 11, which was depositedon the first and second silicon wafers 1A and 1B produced by the processshown in FIGS. 5a and 5b, is removed. Finally, the first and secondsilicon wafers 1A and 1B are thermally bonded to form a driving section(FIG. 5d). Circle 10 in FIG. 5d (enclosed by a broken line) is shown asthe portion that functions as a valve for feeding air. Thus, a microactuator with the structure shown in FIG. 3 is obtained. Finally, acontact pin 4 is formed on the driving section to complete thestructure.

Following is a description of the operating principle of the presentinvention [FIGS. 6 and 7].

FIG. 6 shows a schematic diagram that illustrates the operatingprinciple when Coulomb's force is used as the driving force. Similarly,FIG. 7 shows a schematic diagram that illustrates the operatingprinciple when air pressure is used as the driving force.

First, the operating principle of the present invention will bedescribed referring to FIG. 6. When no voltage is applied between thesilicon wafer 1 and the silicon nitride films 5A and 5B, contact pin 4remains static as its initial position (FIG. 6a). When a voltage isapplied between silicon wafer 1 and silicon nitride film 5A, the siliconnitride film 5A is lowered by Coulomb's force in the direction shown bythe arrow 12. As a result, a difference in height occurs between siliconnitride films 5A and 5B forcing the contact pin 4 placed between siliconnitride films 5A and 5B to tilt towards the right, while the end of thecontact pin moves in the direction of the arrow 13 (FIG. 6b).

When a voltage is applied to silicon nitride films 5A and 5B, the filmsare lowered in the direction of the arrow 12 and 15 until they reach thesame height. Thereafter, contact pin 4 returns to its upright position.(Note: it is important that silicon nitride films 5A and 5B are firstlowered from their initial position). Thus, the end of contact pin 4moves in the direction of the arrow 14 (FIG. 6c).

When the voltage applied to the silicon nitride film 5A is removed, thesilicon nitride film 5A attempts to move back in the direction of thearrow 17, owing to a spring force inherent to its structure. As aresult, the contact pin 4 moves to a position which is a mirror image ofthe position shown in FIG. 6b. Thus, the end of the contact pin moves inthe direction of the arrow 16 (FIG. 6d). When the voltage applied tosilicon nitride film 5B is removed, silicon nitride film 5B tries tomove back in the direction of the arrow by a force inherent to itsstructure. Therefore, the end of the contact pin 4 moves in thedirection of the arrow 18 (FIG. 6e).

As previously described, the micro actuator is operated by the operatingsequence shown in FIGS. 6b through 6d, forcing the end of contact pin 4to rotate in a clockwise rotation.

The operating principle of the present invention is further explained byreferring to FIG. 7. First, a voltage is applied to the silicon wafer 1Bto close the wedge-typed air valve V. By applying Coulomb's force, theair-valve V adheres to the lower silicon wafer 1B. Air is supplied tothe air channel 8 by an air pump (not shown) after closing the air valveV. Air, however, is not supplied to the right air channel A₂ but only tothe left air channel A₁ (as a result of the air valve V being closed).Thus, the upper silicon wafer 1A is raised in the direction of the arrow32 by air pressure in air channel A₁. A difference in height occursbetween the silicon wafers 1A and 1B and the end of the contact pin 4moves in the direction of the arrow 30 (FIG. 7a). When the voltageapplied to the silicon wafer 1B is turned off, the air valve V opens,and air is supplied in the direction of the arrow 34 to both airchannels A₁ and A₂. As a result, the silicon wafers 1A and 1B move inthe direction of the arrow by air pressure in channels A₁ and A₂. Sincea difference in height occurs between the silicon wafers 1A and 1B, thecontact pin 4 returns to its upright position, although its heightdiffers from its initial height. Thus, the end of the contact pin 4moves in the direction of the arrow 36 (FIG. 7b).

When a voltage is applied to the silicon wafer 1B, the wedge-type airvalve V closes, air is released from the left air channel A1, andsilicon wafer 1A is lowered in the direction of the arrow 44. As aresult, because a difference in height occurs between the silicon wafers1A and 1B, the contact pin 4 tilts and its end moves in the direction ofthe arrow 42 (FIG. 7c). Finally, when the air valve V, which had beenclosed in the step illustrated in FIG. 7c reopens, air supplied to theright air channel A₂ is released. The silicon wafer 1B descends in thedirection of the arrow until silicon wafers 1A and 1B reach the sameheight, at which time contact pin 4 returns to its initial position withthe end of contact pin 4 moving in the direction of the arrow 46 (FIG.7d).

As previously described, when air pressure is used as the driving force,the micro actuator follows a sequence similar to the one described inFIG. 6, and the end of the contact pin 4 rotates clockwise.

Though the operating principle of micro actuators using Coulomb's forceand air pressure as driving forces are described above, the same holdstrue for a micro actuator that uses vibrational force as its drivingforce.

A micro positioning device can be structured by arranging the abovemicro actuators on the same surface as an array and arranging a movingmember on the micro actuator array. FIG. 8 shows a schematic diagram ofan X-axis-directional structure of a micro positioning device accordingto a further embodiment of the present invention. This embodiment usesvibrational force as its driving force.

In FIG. 8, a first voltage is applied to a first aluminum electrode 3Aand a second voltage is applied to a second aluminum electrode 3B. Thefirst and second voltages have a predetermined phase difference.Therefore, PZT 2 bonded on the silicon wafer 1 moves vertically or inthe direction of the arrow with the predetermined phase difference. Thevertical motion intermittently causes a difference in height between thefirst aluminum electrode 3A and the second aluminum electrode 3B. Theend of contact pin rotates due to the intermittent height difference inthe direction of the arrow. Therefore, the moving member 15 (e.g. aroller) placed on a plurality of contact pins 4, moves horizontally bymotion of the contact pins 4. When the end of contact pin 4 movesleftward by driving an actuator, the actuator to the left side of theabove actuator is activated, the end of the contact pin 4 movesrightward, and the roller 15 is pressed rightward by the actuator. Thus,the roller 15 is positioned at a certain balanced point.

In the above embodiment, only positioning in the X-axis direction wasdescribed. However, the same is also true for positioning in the Y-axisdirection. Additionally, in the above embodiment, the driving forces usevibrational force. However, the positioning operation is the same asthat of the above embodiment even if other types of driving forces areused, and even if the structure of the micro positioning device of thepresent invention differs.

As described above, the micro actuator of the present invention use adirect driving system directed by a plurality of actuators. It attains ahigh positioning accuracy even for open loop control. It also attainspositioning within an operating range of several tens to severalhundreds of micrometers in the X and Y directions. It is thus possibleto obtain a compact and lightweight miniature micro positioning device.

While the invention has been particularly shown and described withreference to preferred embodiments thereof it will be understood bythose skilled in the art that the foregoing and other changes in theform and details may be made therein without departing from the spiritand the scope of the invention.

What is claimed is:
 1. A micro positioning semiconductor integrateddevice for achieving fine positioning of a friction driven movingmember, comprising:a substrate;; a plurality of micro actuators arrangedon said substrate in an array formation, each of said micro actuatorscomprising:a driving section providing vertical motion, and an elongatedpin having two ends, one of said ends being free moving and the secondcontacting said driving section, wherein the vertical motion of thedriving section drives the free moving end of said pin to rotate arounda horizontal axis; and the moving member is resting on the free movingend of said pins, wherein friction converts the rotational motion of thepins into translational motion of the moving member, thereby providingcontrollable motion and fine positioning in a predetermined direction.2. The micro positioning semiconductor integrated device according toclaim 1, wherein each of said driving sections further comprisesapiezoelectric element connected to said substrate for generating adriving force that converts into vertical motion; and at least twoelectrodes placed on said piezo electric element with said elongatedpin, acting as a contact pin, vertically placed across said electrodes.3. The micro positioning semiconductor integrated device according toclaim 1, wherein said substrate is a silicon wafer.
 4. The micropositioning semiconductor integrated device according to claim 1,wherein said moving member is a rotor.
 5. The micro positioningsemiconductor integrated device according to claim 1, wherein saidpredetermined direction includes the horizontal direction.
 6. The micropositioning semiconductor integrated device according to claim 1,wherein said driving section is formed by a semiconductor fabricationtechnique.
 7. The micro positioning semiconductor integrated deviceaccording to claim 2, wherein said driving force is a vibrational force.8. The micro positioning semiconductor integrated device according toclaim 7, wherein said vibrational force is generated by a piezoelectricelement.
 9. The micro positioning semiconductor integrated deviceaccording to claim 2, wherein said driving force is generated byCoulomb's force.
 10. The micro positioning semiconductor integrateddevice according to claim 2, wherein said driving force is generated byfluid pressure.
 11. The micro positioning semiconductor integrateddevice according to claim 10, wherein said fluid pressure is airpressure.
 12. The micro positioning semiconductor integrated deviceaccording to claim 2, wherein said vertical motion is converted intorotational motion by said contact pin in said actuator.
 13. The micropositioning semiconductor integrated device according to claim 12,wherein said contact pin is made of polyimide.
 14. The micro positioningsemiconductor integrated device according to claim 12, wherein saidcontact pin is made of resist.
 15. The micro positioning semiconductorintegrated device according to claim 1, wherein said actuators movecooperatively to provide micro positioning of the moving member in thepredetermined direction.
 16. The micro positioning semiconductorintegrated device according to claim 1, wherein said array formation ofactuators achieves micro positioning of said moving member in the rangeof tens to several hundredth of micrometers.
 17. The micro positioningsemiconductor integrated device according to claim 2, wherein said atleast two electrodes are aluminum electrodes.